Arc extinguishing fluid



Patented Feb. 23, 1932 barren starts rates-ea rem v seine JOHN D. I-IILLIARD, OF GLENS FALLS, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK ARC EXTINGUISHING FLUID No Drawing.

My invention relates to an arc-extinguishing fluid and more particularly to such a fluid for use in fluid-break circuit interrupters enclosed within a tank or housing.

The use of a dry mineral oil as the arcextingushing and insulating medium in circuit breakers of large interrupting capacity is well known and commonly accepted practice. The oil circuit breaker design, however, has been rendered difficult in many respects by the frequently enormous explosive pressures developed within the switch tank or housing during interruption of the circuit. These tremendous pressures are caused in part by the generation of large volumes of gases by the dissociating action of the power are on the oil. The gaseous pressures so generated may be high but it is possible to design a switch housing sothat it will withstand the pressure caused by arcing of reasonable duration and intensity. Due, however, to the fact that the gases so generated may be highly inflammable or of an explosive nature another source of excess pressure, namely a detonation or secondary explosion, is present. In the usual type of oil switch, there is an air space in the switch tank above the oil level and it is within this space that the inflammable gases collect. Accordingly, if these gases are ignited by a static spark, or by other causes a resulting detonation or secondary explosion may produce such disruptive pressures within the tank that it fails. A severe detonation also may cause excess vibration of the tank so that the porcelain or other insulating material of the bushings for the lead-in conductors is cracked or broken oil". The gas which is formed when an arc is drawn in oil is a mixture of hydrogen, methane, acetylene ethylene and small quantities of other gases. Accordingly, there is a possibility of detonation in the gaseous charge which may produce a pressure or concussion beyond that produced in the ordinary gas explosion and is, therefore, more dangerous to the structure of the breaker.

The are in the oil causes the dissociation of part of the oil, assumed to be decane, into hydrogen and hydrocarbon gases, the heat produced by the are also dissociating the Application filed November 26, 1929. Serial No. 410,008.

molecules of the gases, and it is during the recombination of the atoms with the oxygen in the air space above the oil that detonation is liable to take place. It is possible, of course, that the quantity of acetylene gas produced in the breakers may be comparatively large because the circuit breaker oils is high in. the paraflin series and also is subjected tothe high temperature of the arc. Acetylene, being an endothermic gas, can detonate under pressure alone and a mixture of acetylene and air has a greater range Within which it may explode than any other mixture so that there is a real danger of detonation.

The destructive consequences of a switch failure involving rupture of the oil tank and pro ection of the burning oil and gases throughout the switch station are well known to designing engineers and operators and are guarded against in everypractical manner known.

It is an object of my inventionto provide an arc-extinguishing fluid which shall produce a non-detonating gas when the fluid is acted upon by an electric are.

It is a further object of myinvention to provide an arc-extinguishing fluid comprisinga mixture of a mineral oil and a detonation suppressor for eliminating the disruptive or concussive effect of a detonation in a circuit breaker tank. 1

My invention will be more'fully' set forth in the following description and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexedto and forming a part of this specification. I i

In accordance with my invention,.the detonating effect of the gases generated by the action of :an are on the oil is eliminated by mixing in suitable'proportions with the usual dry circuit breaker oil a detonation suppressor thereby increasing the effective-capacity of the circuit breaker. An example of a detonation suppressor is aniline which when mixed in suitable proportions with the oil does not adversely affect the dielectric strength thereof to a dangerous degree. Benzene, toluene and xylene act in a similar manner as aniline although the latter substance is preferred. Detonation suppressors per se, as well as the relative weights thereof for suppressing detonation, are well known and it is not believed necessary to enumerate fur- 5 ther examples other than to state that my invention is not limited to the specific detonation suppressors above mentioned When the arc-extinguishing fluid comprising a detonation suppressor is to be used in a single tank in which the switch contacts are bridged by a single bridging member, the detonation suppressor should have fairly good dielectric characteristics, as for example ani-' line, so that the dielectric strength of the mixture shall not be so low that there is danger of shorting the contacts; By way of example but without limitation of my invention thereto the dielectric strength of the mixture should not be below 20,000 volts per 0.2 inch.

9; In certain other types .of circuit interrupters wherein a separate container is provided for each movable contact, as where the movable contact separates, from; its coacting contact within the arc-extinguishingfluid and there- 5 after is withdrawn to a position in air above the surface thereof, the dielectric strength of the mixture is not necessarily so important, so that in this case the most effective and suit-V able detonation suppressor .may be used.

9 It shall be understood that my invention is not limited to a mixture of oil with a single detonation suppressor but that two or more of said suppressors may be mixed with the oilwithout departing from the spirit of my 5 invention. a I i What I claim as new and desire to secure by Letters Patent of the United States,-.is:

1. An arc-extinguishing fiuidconsisting of a mixture of a combustible mineral. oil and a detonation suppressor. I

2. An arc-extinguishing and insulating fluid comprising a mixture ofa combustible dry mineral oil'and a substance'forpreventing detonation of gases formed by the action of an are on sai oil, said mixture having comparatively high dielectric, strength.

3. An arc-extinguishing fluid for fluidbreak circuit interrupters having a tank sub-' ject to expansive pressures during circuit interruption comprising a mixture of a combustible mineraloil and a substance for preventing detonation of gases produced by the action of an arc on said'oilr 4. An arc-extinguishing and insulating me- 56. dium for a circuit interrupterlof the fluidbreak type, comprising in combination a mixture of a detonation suppressor and av substantially dry combustible, mineral oil, the dielectric strength of the mixture being at least 20,000 volts per-0.2 inch.

In witness whereof, I have hereunto set my hand this 23rd day of November, 1929.

- JOHN D. HILLIARD. 

